1. Field of the Invention
The present invention relates to an arrangement for transmitting a torque from a power tool to a working tool releasably connectable with the power tool and including a shank forming part of the working tool and a chuck for receiving the shank and forming part of the power tool, with the shank and the chuck having cooperating elements which provide for joint rotation of the chuck and the shank.
2. Description of the Prior Art
For forming bores in hard constructional components formed of concrete, stone, or the like, working tools with a tubular support, which is provided at its free end with a plurality of cutting elements, are used. The working tool is releasably connected with a power tool and is rotated by the power tool drive. For transmitting the torque to the working tool, an arrangement, which is formed of the working tool shank and a chuck provided on the power tool, is used. Such an arrangement is disclosed, e.g., in German Publication DE-34 34 076.
In DE-34 34 076, the shank is provided at an end of a tubular support opposite to the free end of the tubular support provided with cutting segments. In DE-34 34 076, the shank has a first region conically widening in an operational direction of the working tool, a second region adjoining the first region facing in the operational direction, the second region having a circumferential groove, a third region adjoining the second region at an end of the second region facing in the operational direction, a fourth cylindrical region adjoining the third region at an end of the third region facing in the operational direction, and at least two drive grooves extending parallel to a working tool axis over all of the shank regions.
The chuck of DE-34 34 076 has an opening conically widening in the operational direction of the working tool for receiving the shank, two locking elements projecting into the receiving groove for engagement into the circumferential groove of the chuck, and at least two drive dogs projecting into the receiving groove for engagement in the drive grooves of the shank. The locking elements are displaceable substantially radially by a locking sleeve displaceable parallel to the operational direction.
Upon insertion of the working tool shank in the chuck, centering of the shank in the chuck and a tight clamping of the shank in the chuck take place as a result of cooperation of conical regions of the shank with respective regions of the chuck. The locking elements, which engage in the circumferential groove formed in the shank upon the insertion of the shank in the chuck, prevent axial displacement of the shank in the receiving opening of the chuck. The transmission of the torque is effected with the drive dogs which formlockingly engage in the drive grooves provided in the shank.
When a very high torque is being transmitted, the surface pressure between the drive dogs and the drive grooves becomes very high, which can result in the damage of the drive dog flanks associated with respective surfaces of the drive grooves of the shank.
Accordingly, an object of the present invention is to provide an arrangement with which very high torques can be transmitted without any or a minimal damage of the torque-transmitting elements, while insuring that guiding, centering, clamping, and sealing functions, in the area of a contact of the first shank region with the respective chuck region, are maintained.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing at least one additional drive groove in the shank, which extends in the third and fourth regions of the shank, and by providing, in the chuck, at least one additional drive dog projecting into the chuck receiving opening for engagement in at least one additional drive groove which is formed in the shank.
The additional drive groove according to the present invention is provided in that region of the shank where, because of a large diameter of the respective section of the shank, large torques can be transmitted particularly well. The additional drive groove, which is provided in addition to drive grooves, increases the engagement surface designated for receiving the torque. The increase of the torque-receiving engagement surface of the shank results in reduction of the surface pressure. The reduction of the surface pressure eliminates or substantially reduces the danger of the drive grooves or the drive dogs being damaged. Because the additional drive groove is located only in the third and fourth shank regions, the contact surface, which is available in the first, conical region of the shank remains unchanged and, in cooperation with respective surface of the chuck, provides for necessary guidance, centering, clamping, and sealing.
Preferably, the number of additional drive grooves corresponds to the number of drive grooves, with each additional drive groove being located between two drive grooves. With an increased number of all of the drive grooves, an entire torque-receiving engagement surface of the shank is increased which results in decreasing of the surface pressure.
A uniform distribution of an acting on the shank, torque over the circumference of the shank is advantageously achieved by providing three drive grooves uniformly distributed over the shank circumference, and three additional drive grooves likewise uniformly distributed over the shank circumference, with each additional drive groove being arranged between respective two drive grooves.
For quick insertion of the working tool shank into the chuck without spending much time for aligning the drive grooves and the additional drive grooves with respective drive dogs, advantageously each additional drive groove is equidistantly spaced from the adjacent drive grooves. E.g., with three drive grooves and three additional drive grooves, the grooves are arranged relative to each other at angle of 60xc2x0.
To make the torque-receiving engagement surface of the shank as large as possible, the circumferential extent of each additional drive groove is so selected that it corresponds to 0.3-0.8 of the circumferential extent of the drive groove. The radial depth of each additional drive groove is so selected that it corresponds to 0.3-0.6 of the radial depth of a drive groove.
In the transition region between the shank and the tubular support, there is provided a flange-shaped widening the outer diameter of which corresponds to the outer diameter of the tubular support.
Under certain conditions, when the additional drive grooves also perform an encoding function, it is advantageous when the angles between adjacent drive grooves, and/or their radial depths, and/or their circumferential extents differ from each other. The presence of the encoding function permits to associate, e.g., working tools having different diameters with power tools having different powers. E.g., a working tool having a small diameter can only be used with or be inserted into a power tool with a small driving power.
For a uniform distribution of the transmittable torque over the entire circumference of the working tool shank, the chuck advantageously has a number of additional drive dogs corresponding to the number of drive dogs, with each additional drive dog being located between two adjacent drive dogs.
For quick insertion of the working tool shank into the chuck without spending much time for aligning the shank with the chuck, advantageously, each additional drive dog is equidistantly spaced from adjacent drive dogs. As a result of the uniform distribution of the drive dogs, the shank can be inserted by being pivoted only by a small angle until the drive dogs engage in the drive grooves, and the additional drive dogs engage in the additional drive groove.
In order for the chuck to be able to transmit a torque as large as possible, the circumferential extent of each additional drive dog is so selected that it corresponds to 0.3-0.8 of the circumferential extend of the drive dog, and the radial height of each additional drive dog is so selected that it corresponds to 0.3-0.6 of the radial height of the drive dogs.
The length of the additional drive dog substantially corresponds to the length of the additional drive groove.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of the preferred embodiment, when read with reference to the accompanying drawings.